If you want your Line item to aim for a specific viewability threshold, check the ‘Enable Viewability Targeting’ box, and enter the viewability threshold you wish to target in the ‘Viewability Target’ area.
This is not a guarantee, but rather a benchmark. The platform will determine how likely an impression is to be viewable through pre-bidding technology. Per IAB guidelines, an ad is considered viewable if 50% of the pixels are in-view for 1 second or more. Using a high threshold may limit delivery of the Line. While the IAB benchmark is 70%, this may limit the number of impressions that can be won causing the campaign to under pace. If you are using a viewability threshold bids should be greatly increased. If viewability is an important metric for you, you can also try running smaller Creatives or native ads as they tend to have higher viewability.